This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-72549, filed on Mar. 15, 2000 and No. 2000-277823 filed on Sep. 13, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly it relates to the damp-proof structure of a liquid crystal display device.
2. Description of the Background
In recent years, a liquid crystal display device has been widely used as a display device in portable information equipment because of its characteristics including lightweight, its small thickness and low power consumption. In order to obtain a bright and brilliant image, it is now becoming mainstream practice to employ an active matrix type liquid crystal display device having thin film transistors (TFT) arranged as a switching device at respective pixels.
Among various liquid crystal display devices, those that are used indoors can be sufficiently isolated from moisture by an ordinary sealing member covering the outer periphery of a liquid crystal cell. Thus, it is difficult to cause decreases in voltage retention, which bring about obstruction when driving the TFT, in such devices. However, with respect to those that are mainly used outdoors, such as in portable information equipment, the environment surrounding a given liquid crystal display device is far severer than those used indoors.
In recent years, liquid crystal display devices have been used in marine applications such as in small boats. Such devices are particularly attractive because of they can be installed in diverse locations particularly in small boats used in marine leisure activities. For example, such devices are often used as display devices in fishfinders, radars and GPS devices. Because the display devices are subjected to severe environments, isolation of the structures of the devices from moisture sometimes is not sufficient using conventional sealing members, thereby resulting in deterioration of the device properties, such as decreases in resistance of the liquid crystal. This decrease in resistance results in substantial deterioration of the display performance, thereby decreasing the service lives of the devices. Even in the case of liquid crystal display devices used indoors, penetration of moisture into the interior of the liquid crystal display devices occurs after use for long periods of time.
Normally, a waterproof frame comprising a polymer member is attached on the outside of the liquid crystal display portion in order to solve the problem. However, the conventional waterproof frame has a large outer dimension and a heavy weight in order to increase the waterproofing performance. Another problem is that since the proportion of the display region with respect to the area of the outer frame is decreased, it is difficult to see the display device. Furthermore, while the conventional waterproofing frame can effectively prevent liquid water from penetrating display devices, it is not very effective in preventing penetration of water vapor molecules acting. That is, water vapor molecules penetrate through the network structure of the polymer even in small amounts thereby invading the display region. Therefore, upon exposure to an environment of high humidity, there is the possibility of deterioration in display quality because of a decrease in voltage retention.
This problem becomes significant in liquid crystal display devices of the guest-host type (GH type liquid crystal) described below. GH type liquid crystals have attracted attention because of their wide viewing angle. The GH type liquid crystal is formed by dissolving a dye having a large dichroic ratio in a liquid crystal. Particularly, in recent years, because of the increased demand for color display devices, the development of GH type color liquid crystal display devices is earnestly conducted. However, the reliability of the GH type liquid crystal is very hard to maintain, because the GH type liquid crystal suffers reduction in voltage retention because of several factors, such as the decomposition of dye molecules and contamination by ionic impurities. Furthermore, a polar compound, such as a dye, can extract inorganic ions from glass substrates. When water intervenes, the mobility of the extracted inorganic ion notably increases, which results in a rapid loss of electrical resistance thereby greatly reducing the voltage retention. Accordingly, the extent of reduction in voltage retention of the GH type liquid crystal caused by the invasion of water becomes far larger than for other liquid crystals. There is no solution to the problem, and thus it is the present situation that the practical application of a liquid crystal display device of the TFT driven using the GH liquid crystal is delayed.
Accordingly, one object of the present invention is to provide a liquid crystal display device with savings in weight and which permits miniaturization and to provide a liquid crystal display device which is effective in preventing deterioration of display quality because of moisture penetration.
Another object is to provide a liquid crystal display device having high reliability that can maintain excellent display quality.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a liquid crystal display comprising:
a substrate;
a liquid crystal layer disposed on the substrate; and
a sealing part surrounding the liquid crystal layer and disposed on the substrate, wherein the sealing part comprises a hygroscopic solution.
The term xe2x80x9cdisplay qualityxe2x80x9d herein means that an image display of high speed and brilliant color display can be conducted. A gauge of reliability is that little deterioration takes place.
The sealing part of the liquid crystal display of the present invention comprises a hygroscopic solution.
The sealing part may comprise an inner sealing part and an outer sealing part, with the hygroscopic solution disposed between the inner sealing part and the outer sealing part.
The liquid crystal display may further comprise a first inlet of the liquid crystal layer; and second inlets of the hygroscopic solution next to the first inlet.
The liquid crystal display may further comprise a first inlet of the liquid crystal layer; and second inlets of the hygroscopic solution on the opposite side of the substrate disposed at the first inlet. The hygroscopic solution may be the same liquid crystal as the liquid crystal layer.
The hygroscopic solution may comprise suspended hygroscopic compound particles. The liquid crystal display may further comprise a counter substrate disposed on the liquid crystal layer.
The sealing part may comprise polymer particles which involve the hygroscopic solution. The hygroscopic solution may be a guest-host type liquid crystal.
The sealing part may further comprise a polymer seal wall.
The polymer particles may be in the form of fine particles and the polymer particles may have an average diameter of 3 micrometers.
The hygroscopic solution may comprise at least one material selected from the group consisting of P2O5, Mg(ClO4)2, SiO2, CaSO4, CaCl2, and CuSO4.
The liquid crystal layer may consist of a guest-host type liquid crystal.
The hygroscopic solution may comprise a silicone oil and a guest-host type liquid crystal. The hygroscopic solution can take in vapor and change the vapor to liquid.
The present invention provides a liquid crystal display comprising: a pair of substrates; a liquid crystal layer disposed between the substrates; a sealing part surrounding the liquid crystal layer and disposed on the substrates; and a protective layer covering the pair of substrates and the sealing part.
The sealing part may comprise an inner sealing part; an outer sealing part, with the hygroscopic solution disposed between the inner sealing part and the outer sealing part.
The sealing part may comprise polymer particles which involve the hygroscopic solution.
When the liquid crystal cell as described above is exposed to an environment of high humidity, the second sealing part is exposed to water vapor molecules, but even though the water vapor molecules penetrate through the second sealing part, the small amount of water vapor molecules are caught by the filler in the second region, and thus they do not penetrate the first sealing part, thereby preventing invasion of water into the liquid crystal cell. The filler is a hygroscopic solution.
When the liquid crystal cell is exposed to an environment of high humidity, the halogenated ethylene resin covering the entire outside of the cell is exposed to water vapor molecules, but because the halogenated ethylene resin has excellent damp-proof properties, the water molecules do not penetrate the cell thereby preventing invasion of water into the liquid crystal cell.